Significant portions of known oil reserves are bound in formations requiring enhanced oil recovery (EOR) techniques for effective and efficient extraction. Such reserves exist in previously untapped fields as well as in fields where traditional oil recovery has reached a practical limit.
Among EOR techniques are steam-driven recovery methods, and non steam-driven recovery methods. Steam-driven approaches include the Steam-Assisted Gravity Discharge (SAGD) technique. Non steam-driven approaches include for example water flooding and chemical flooding.
Water flooding comprises sweeping oil from oil-bearing formations by injecting large volumes of water into the formations and extracting the resulting oil-water mixture topside for processing. Generally, even after such water flooding techniques have been used on a field, at least 40% of the Original Oil In Place (OOIP) remains in the formation.
Chemical flooding has been found useful in extracting additional oil after other techniques have reached their practical limits as well as in virgin fields. Practical limits are often based on limited water supply. While chemical flooding utilizes water, the chemical treatments reduce water requirements, while increasing oil recovery. Chemical flooding techniques include for example polymer flooding.
Polymer flooding comprises using specific polymers, particularly for enhancing recovery by viscosity adjustment. Additional chemicals can be used, such as surfactants, (co)solvents, alkaline compounds, and/or stabilizing compounds. While these chemicals may be used separately in aqueous solutions, considerable experience has developed in using them in combination in aqueous solutions. Such combination treatments are sometimes referred as Alkali-Surfactant-Polymer (ASP) or Surfactant-Polymer (SP) treatments. For some fields, such treatments have been observed to result in an additional 15% to 30% extraction of the OOIP in the formation on top of water flooding.
Different polymer techniques have been developed for injection into subterranean oil fields. It is known e.g. from WO 2010/133258 an aqueous solution comprising anionic or amphoteric water soluble polymer and stabilizing agent for preventing the chemical degradation once the polymer is introduced into the injection fluid.
When extracting oil using water flooding or chemical flooding techniques, there is the need for treating the oil-water mixture extracted from the oil-bearing formations. Such treatment processes aim first at separating the oil from the water. Such treatment processes also aim at treating the produced water before being disposed of, and/or before reinjection into the injection well as injection water.
Different oil-water mixture treatment techniques have been developed.
It is known e.g. from WO2014/151641, a method for recovering oil from an oil-bearing formation and treating produced water containing an anti-scalant compound. Said method particularly comprises the step of directing the produced water through a ceramic membrane to remove oil from the produced water, and for obtaining a permeate stream and a retentate stream. Prior the membrane filtration step, said method comprises several steps, including recovering an oil-water mixture, separating oil from the oil-water mixture, deactivating the anti-scalant compound, optionally precipitating and settling solids.
It is also known e.g. from WO2014/151242, a process for recovering oil from an oil-bearing formation. Said method particularly comprises the step of directing the produced water to a ceramic membrane, for obtaining a permeate stream as well as a retentate having suspended solids, hardness compounds, free oil and emulsified oil. Prior the membrane filtration step, said method comprises recovering an oil-water mixture, separating oil from the oil-water mixture, optionally carrying out an ion exchange filtration. After the membrane filtration step, said method comprises chemically treating the permeate stream, optionally mixing a polymeric compound with the permeate stream, optionally mixing an alkali compound with the permeate stream, optionally mixing a surfactant compound with the permeate stream, optionally carrying out an ion exchange filtration on the permeate stream, and injecting the permeate stream into the oil-bearing formation.
Different types of ceramic membranes are known in the art. It is known e.g. ceramic membrane technologies from U.S. Pat. Nos. 5,611,931 and 6,767,455.
It is known techniques for recovering and treating oil-water mixtures, and produced water obtained from it. The treatment of the produced water usually shows to be challenging, particularly considering the high viscosity of the produced water. Up to now, the techniques for treating the produced waters, obtained from chemically enhanced oil recovery processes, have not shown sufficiently satisfactory. Particularly, it is not known so far conventional treatment processes for treating the produced water obtained from those processes relying on the use of viscosity-increasing polymers. Indeed, known processes have shown limited efficacy, if not at all, for separating water (in the permeate) from suspended solids, free oil, grease and emulsified oil (in the concentrate), while allowing the recycling of the polymers. Such processes do not usually allow obtaining a permeate, comprising the polymer. As a consequence, such processes do not usually allow recycling most of the polymer comprised into the produced water, for subsequent reinjection into the oil-bearing formation.